A Belfort to Paris passes at the only spot of the Line 4 where you can frame the train together with the Vosges Mountains behind. This is the famous "Ligne Bleue des Vosges" (the Vosges blue horizon line), an expression that means the French border between 1871 and 1918 when the Alsace and Lorraine regions had been captured by Germany after France lost the 1870 war.